This report describes an investgiation of the performance of a trial embankment constructed in an area of high rainfall on the route of the M6 motorway extension between Lancaster and Penrith to provide information for the design and specification of the motorway. The embankment, 6 metres high with 1-in-2 (27 degrees) side slopes, was constructed using low-permeability boulder clay placed in a much wetter condition than would normally be specified or permitted for earthwork fills. Horizontal drainage blankets of specially graded crushed rock were incorporated at different spacings within the fill. Measurements of pore pressure, in-situ permeability and settlement were made to determine the full-scale consolidation characteristics of the wet fill and to assess the performance of the horizontal drains in accelerating pore-pressure dissipation. The trial demonstrated that it is possible to construct stable embankments up to 6 meters in height even when the boulder clay is used at the highest moisture content at which earth-moving plant can be operated. It was concluded that the drains were not very effective as a means of accelerating the dissipation of pore pressures during construction, and so did not contribute to the stability of the embankment; and they were unnecessary from the point of view of accelerating settlement after construction as the recorded movements were too small to be of any practical concern. (A)

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